The compound 4,4'-bis(4-p-sulfoanilino-6-isopropanolamino-s-triazin-2-ylamino)-2,2'-sti lbenedisulfonic acid tetrasodium salt is one of the preferred fluorescent whitening agents, also known as optical brighteners. Brighteners are particularly useful for application to cellulosic fibers such as papers and textiles for imparting improved appearance.
The specific brightener, 4,4'-bis(4-p-sulfoanilino-6-isopropanolamino-s-triazin-2-ylamino)-2,2'-sti lbenedisulfonic acid tetrasodium salt, is particularly useful for textiles that have been impregnated with thermosetting resins conventionally used for imparting wash and wear qualities and crease resistance to fabrics.
A prime advantage of this compound is that it can be applied simultaneously with these resins to the textile substrates. However, the brightener preparations resulting from previous methods of synthesis either contained interfering impurities or were not sufficiently stable for uniform application.
Bis-triazinyl stilbenedisulfonic acid-based fluorescent whitening agents (FWA) have been known since about 1940 (Alien Property Custodian Specification Ser. No. 381,856, published May 11, 1943). Various of these FWA have been synthesized and selected industrially based upon their affinities to specific substrates or to agents used for impregnating or coating specific cellulosic substrates or matrices.
British Pat. No. 896,533 (1962) to Sandoz taught the whitening of paper with the subject FWA in solution or suspension due to its miscibility with sizes used in paper manufacture. In this reference other FWA's in aqueous solution are specifically taught to be useful in whitening cotton textiles.
U.S. Pat. No. 3,532,692, issued Oct. 6, 1970, teaches that the p-sulfoanilino and diisopropanolamino are preferred substituents on the bis-triazinyl stilbenedisulfonic acid matrix but does not specifically mention the subject FWA of this invention in its description of the invention therein. That invention was directed to the manufacture of FWA by condensation of appropriate stilbenes with cyanuric chloride in strongly acidic aqueous media.
U.S. Pat. Nos. 3,239,513 and 3,360,479, assigned to Geigy and based on a 1959 Swiss patent application, teach fluorescent whitening agents having amine substitutents, similar but not identical, and are not symmetrical. Instead of diisopropylamine, N-alkyl alkanolamine or N-alkyl alkandiolamine are taught. They are noted to have high affinity for aluminum salts, sulfates and silicates used as paper fillers. The latter patent teaches stabilization of solutions of these optical brightening agents by the use of organic solubility promoters to ensure uniform distribution of the brightening agent during use. The concommitant use of synthetic resins in the paper is also taught. Thus, the preparation of a resin-reinforced, felted fabric containing FWA(optical brightener) maintained in aqueous solution by the use of co-solvents during impregnation is well disclosed.
U.S. Pat. No. 3,766,083 issued Oct. 16, 1973 teaches the specific FWA of this invention as a fluorescent whitening agent for whitening cellulosic fibers concommitantly with their treatment with conventional termosetting textile resins and is also directed to the stabilization of the aqueous solution of the specific FWA by the addition thereto of a co-solvent. While the use of the cosolvent facilitates uniform application of the FWA, these materials also weaken (or plasticize) the polymer chains and their substantivity to the cellulosic fibers.
Investigation into the use of the FWA solutions shows that the pure specific FWA agent does not destabilize in aqueous solution. Certain unidentified organic impurities, found on HPLC chromatography, as well as residual salt formed during synthesis of the FWA cause the destabilization with haziness of solution, precipitation of solution contents and non-uniform deposition on the fibers as well as impurity of the color of the deposited FWA pigment.